X-ray film copying is required to provide duplicate information and documentation to various entities. Accurate copies, with definition and resolution of substantially the same quality as the original, are particularly sought in the environment of medical X-rays, which may be required for making many of the most critical decisions. Prior art X-ray copying devices have produced copies with reduced resolution either because of air trapped between the original film and the copy film during exposure or the occurrence of creep between the original and copy films during exposure.
The copying of photographic films is performed in a darkroom environment. One form of photographic films are X-rays, with medical X-rays representing the greatest volume, both with respect to the number of X-rays generated and the need for multiple copies. The copying of X-ray films is usually accomplished using a "black light" fluorescent tube emission source which emits a high concentration of short wave length ultraviolet radiation for exposing the copy film roughly matching the spectral responses of the illuminator and film. In one copying technique the original and copy films are pressed against a glass plate and either the plate is moved past a stationary light source or the light is moved to expose the copy film retained against the stationary plate, resembling flat bed plain paper document office copiers. However, this technique causes air to be trapped between the films and pressing the films between two flat surfaces causes the trapped air to be compressed rather than being expunged from the interface between the films. These small pockets of air remain to cause distortion and diminished resolution of the copy of the X-ray film.
Another technique used to copy X-ray films is to wrap the developed film original and the overlying undeveloped film on a transparent drum using a belt that partially wraps about the drum to retain the films in intimate contact as the copy is exposed, using a light source disposed within the drum. Although this method is better adapted to urge trapped air from the interface between the films, the manner in which films are usually wrapped about the drum periphery causes creep between the films as the undeveloped film is disposed at a slightly greater radius as the pair of films is curved over the drum. The relative movement between films is material, causing significant diminution of the resolution of the copied image with the impairment increasing with the length of the document being copied. Even if relative movement were eliminated, the difference in radii during exposure would cause some distortion.